The present invention relates to a system for providing accurate edge alignment of boxes being conveyed sequentially or in a shingled configuration and, more particularly, to a system for simultaneously squaring and aligning a moving line or a shingle of knocked down corrugated paperboard boxes for accurate longitudinal slitting.
In accordance with the current state of the art, corrugated paperboard running in a continuous web or sheet is most commonly slit in a longitudinal direction by running the board through a slitting nip formed by a pair of overlapping upper and lower blades which operate in a shear-type mode to provide a continuous slit. Such shear-type slitting techniques work satisfactorily for standard single thickness corrugated paperboard sheets, but slit quality deteriorates rapidly with double and triple wall sheet and when slitting multiple layers, such as may be encountered in a folded and glued container, sometimes referred to as a knocked down box.
More recently, the assignee of the present invention has developed alternate slitting apparatus and methods which overcome the thickness limitations inherent in shear-type slitting and, therefore, provide means for slitting not only multi-layer paperboard products, but also slitting a shingle of overlapping sheets of corrugated board. In particular, U.S. Pat. No. 5,165,314, entitled "Slitting Shingled Sheets" filed on Sep. 20, 1991, and U.S. Pat. No. 5,158,522, entitled "Slitting Corrugated Paperboard Boxes, filed on Sep. 20, 1991, both of which are commonly owned with the invention described and claimed herein, describe methods and apparatus for accurately and efficiently slitting knocked down corrugated boxes being conveyed in a shingle. Such shingle slitting techniques provide potentially great benefits to the corrugated paperboard box industry by allowing high speed and accurate slitting which is impossible with prior art shear-type slitters, eliminating many intermediate processing steps necessary by the limitations inherent in prior art slitting, and expanding significantly the productivity of a flexo-folder-gluer in which corrugated boxes are made.
Nevertheless, when slitting a shingle of knocked down corrugated boxes, particularly immediately after the boxes are discharged from the flexo-folder-gluer, the maintenance of accurate alignment of the boxes in the shingle is critically important as the shingle is moved into the unitary high speed slitting blade disclosed in the above identified applications. In addition, before the glue has set on the knocked down boxes, the boxes are sometimes subject to so-called "fish tailing" manifested by a loss of square because of slipping of the glued tabs on the overlapping box surfaces to which they are attached. If the shingle is not in accurate alignment, i.e. if the lateral edges of the boxes forming the shingle are not accurately aligned in a vertical plane, or if some of the boxes in the shingle are not square, the subsequent longitudinal slitting of the shingle will result in dimensional inaccuracies and the generation of scrap. Even if knocked down corrugated boxes are not shingled for slitting, but instead conveyed serially in a line, box alignment and square must still be maintained for the slitting operation which follows.